1. Field of the Invention
The present invention relates to high frequency modules provided with a plurality of filter devices.
2. Description of the Related Art
In general, a mobile apparatus or the like having a wireless communication function includes a filter circuit that passes only a high frequency signal of a desired frequency and attenuates high frequency signals having frequencies other than the desired frequency.
For example, Japanese Unexamined Patent Application Publication No. 2012-109818 discloses a filter circuit including a plurality of surface acoustic wave (SAW) filters. To be more specific, in the filter circuit disclosed in Japanese Unexamined Patent Application Publication No. 2012-109818, the plurality of SAW filters are connected in series between an input terminal and an output terminal. Further, additional SAW filers are connected between the ground and each connection line with which the SAW filters are connected in series.
In the filter circuit disclosed in Japanese Unexamined Patent Application Publication No. 2012-109818, an inductor or a series circuit of an inductor and a capacitor (called a “correction circuit”) is connected in parallel to the series circuit of the SAW filters to improve attenuation characteristics outside a pass band. In this case, the correction circuit is adjusted such that a high frequency signal outside the pass band (suppression target signal) propagating in the circuit formed of the SAW filters and a suppression target signal propagating in the correction circuit have the same amplitude in magnitude and have opposite phases to each other. With this, the suppression target signals cancel each other out at a connection point between the circuit formed of the SAW filters and the correction circuit, and are not outputted from the output terminal.
However, in the above configuration, in addition to the circuit formed of the SAW filters having a principal filter function, only to improve attenuation characteristics, the correction circuit formed of an inductor or a series circuit of an inductor and a capacitor needs to be provided.
This increases the number of constituent elements of the filter circuit and consequently makes the filter circuit large in size. Therefore, the above filter circuit is not suitable for use in today's mobile terminals and the like required to be compact.